Left Ventricular Mechanics and Myocardial Blood Flow: LV Diastolic Performance

Although dP/ dtmax did not change, its correlation to end diastolic volume (dP/dtmax-Ved), which is a preload-insensitive and afterload-insensitive contractile index, improved during AAI pacing (73.48 ± 3.2 mm Hg/s/mL vs 77.48 ± 4.7 mm Hg/s/mL, respectively; p = 0.002).
There were no statistically significant differences in cardiac and stroke index, SW, LV Pes or Ves, and MVo2 (Table 2).
Of the diastolic performance indexes evaluated in our study, only dP/dtmin was altered significantly following the restoration of a normal ventricular activation sequence ( — 1,509 ± 160 mm Hg/s vs — 1,550 ± 177 mm Hg/s, respectively; p = 0.038). However, more specific indexes of diastolic function, such as t, showed no clear change (44.0 ± 5.6 ms vs 45.4 ± 4.7 ms, respectively; p = 0.105) [Table 2]. read only
Coronary Flow and CFR Measurements
No patient had any mild or severe arterial obstruction in any region of a vessel where measurements were obtained.
Left Anterior Descending Artery
The restoration of the normal activation sequence caused a slight but nonsignificant increase in baseline coronary flow (increase, 145.0 ± 30.1 to 157.6 ± 32.7 mL/min; p = 0.083), while the coronary flow during maximal hyperemia did not change significantly (346.7 ± 77.9 mL/min vs 341.0 ± 71.0 mL/min, respectively; p = 0.421). As a result, CFR also did not change significantly (2.5 ± 0.7 vs 2.3 ± 0.6, respectively; p = 0.326) [Table 3].
Dominant Coronary Artery
In five patients, the dominant artery was the right coronary artery, while in the other three patients the dominant artery was the circumflex artery. The restoration of a normal activation sequence caused a significant increase in baseline coronary flow (increase, 46.6 ± 14.1 to 71.7 ± 27.5 mL/min; p = 0.002), while the coronary flow during maximal hyperemia did not change (178.2 ± 57.8 mL/min vs 177.1 ± 55.7 mL/min, respectively; p = 0.511), resulting in a significant reduction in CFR (reduction, 3.5 ± 1.0 to 2.6 ± 0.5; p = 0.019) [Table 3 and Fig 2].
Fig2
Figure 2. Doppler recording of coronary blood flow velocity (in centimeters per second) in the circumflex artery during DDD pacing (left panels) and AAI pacing (right panels). During AAI pacing, the coronary flow is increased compared to DDD pacing at baseline (top left, A, and top right, B), while it remains constant during hyperemia (bottom left, C, and bottom right, D). Volumetric flow corresponds to the product 0.5 X average peak velocity X cross-sectional area. The cross-sectional area remains constant in both cases.
Table 2—LV Mechanics During Long-term DDD Pacing and Immediately After Switching to AAI Pacing Mode

Parameters Pacing Mode p Value
DDD AAI
General
Heart rate, beats/min 65.42 ± 10.42 64.97 ± 7.03 0.103
QRS duration, ms 204 ± 16 91 ± 6 < 0.001
Stimulus-to-R interval, ms 137 ± 14 215 ± 5 < 0.001
LV systolic performance indexes
Ves, mL 61 ± 11.68 58 ± 11.23 0.129
Pes, mm Hg 96.6 ± 17.5 95.2 ± 17.1 0.205
Stroke index, mL/m2 46 ± 10.5 47 ± 11.4 0.734
Cardiac index, L/min/m2 4.42 ± 0.43 4.29 ± 0.63 0.574
LVEF, % 46 ± 4.7 49 ± 4.7 0.002
SW, mm Hg/mL 5,694 ± 768 5,494 ± 426 0.517
PRSW, mm Hg 91.8 ± 6.1 100.9 ± 12.3 0.033
dP/dtmax, mm Hg/s 1449 ± 129 1439 ± 122 0.759
dP/dtmax-Ved slope, mm Hg/s/mL 73.48 ± 3.2 77.48 ± 4.7 0.002
Ees, mm Hg/mL 4.287 ± 0.28 5.503 ± 0.60 0.003
LV mechanical efficiency indexes
Ea, mm Hg/mL 2.88 ± 1.03 3.05 ± 1.19 0.273
Ventriculoarterial coupling index 1.63 ± 0.51 2.00 ± 0.64 0.009
MVO2, mL O2/min/100 g 7.055 ± 0.74 7.058 ± 0.73 0.993
LV diastolic performance indexes
Ved, mm Hg 136 ± 17 133 ± 16 0.427
End-diastolic pressure, mm Hg 10.55 ± 0.8 10.59 ± 1.2 0.935
dP/dtmin, mm Hg/s – 1,509 ± 160 – 1,550 ± 177 0.038
t, ms 44.0 ± 5.6 45.4 ± 4.7 0.105

Table 3—Coronary Blood Flow Measurements at Baseline and at Maximal Hyperemia During DDD and AAI Pacing Modes

Parameters Left Anterior Descending Artery Dominant Coronary Artery
DDD AAI p

Value

DDD AAI p

Value

Baseline coronary blood flow, mL/min 145.0 ± 30.1 157.6 ± 32.7 0.083 46.6 ± 14.1 71.7 ± 27.5 0.002
Hyperemic coronary blood flow, mL/min 346.7 ± 77.9 341.0 ± 71.0 0.421 178.2 ± 57.8 177.1 ± 55.7 0.511
CFR 2.5 ± 0.7 2.3 ± 0.6 0.326 3.5 ± 1.0 2.6 ± 0.5 0.019
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